Flash spinning apparatus



,1966 H.J. HOLLBERG I 3,277,526

FLASH SPINNING APPARATUS Filed June 1, 1964 FIG.!

INVENTOR HERBERT JOHN HOLLBERG ATTORNEY United States Patent 3,277,526 FLASH SPINNING APPARATUS Herbert John Hollberg, Richmond, Va., assignor to E. I. du Pont de Nernours and Company, Wilmington, De]., a corporation of Delaware Filed June 1, 1964, Ser. No. 371,259 2 Claims. (Cl. 18-8) This invention concerns improved apparatus for the spinning of a continuous fibrillated strand. In particular, it concerns such spinning apparatus utilizing an improved baflle for spreading the spun strand into a wide web.

A method for producing continuous flbrillated strands is described in Blades et al. US. Patent 3,081,519. The strands are formed by extruding a homogeneous solution of a fiber-forming polymer in a liquid which would be a non-solvent for the polymer at temperatures below the normal boiling point of the liquid. The solution is extruded at a temperature far above the boiling point of the liquid, and at autogenous pressures or greater into a medium of lower temperature and substantially lower pressure. The vaporizing liquid within the extrudate forms bubbles, breaks through confining walls, and cools the extrudate, causing solid polymer to form therefrom. The resulting multifibrous yarn-like strand has an internal fine structure or morphology which may be characterized as a three-dimensional integral plexus consisting of a multitude of essentially longitudinally extended interconnecting random length fibrous elements, hereafter referred to as film-fibrils, which have the form of thin ribbons of a thickness less than 4 microns.

The strands of Blades et al. may be collected in the form of nonwoven sheets according to the methods described in Belgian Patent 625,998. The Belgian patent describes the formation of film-fibril sheets by the random overlapping deposition of continuous fibrillated strands on a moving surface. In order to form more uniform sheets the fibrils in the strands are opened up by directing the strand against a bafile immediately upon issuing from the spinneret orifice. The baffle operating in conjunction with the rapidly expanding solvent gas causes the film-fibril elements to disperse so as to create a wide plexifilament web. The wide web is laid in overlapping multidirectional layers on the moving surface and is then pressed or otherwise treated to form a coherent sheet material.

The process of the Blades et al. patent requires solution temperatures which are above the melting point of the polymer. Because of this, bafiies as heretofore employed have tended to collect melted polymer when the supply of polymer solution to the spinning orifice was stopped, e.g. to temporarily shut-down the spinning operation. When such a deposit was encountered the baflle had to be manually cleaned before the spinning operation could resume. The deposits were difficult to remove and, hence, frequently resulted in considerable and costly delays. If not suitably removed, they could give rise to non-uniformities in the web during the next start-up of the spinning operation. However, as long as the baffle was free of deposits during the initial start-up, the spinning operation continued satisfactorily since, apparently, the baffle was being cooled by expanding solvent gases which flowed rapidly over the surface thereof. When the operation was shut-down and an adequate flow of solvent gas Was no longer available, polymer in the last portion of the discharged solution tended to collect on the bafile and finally solidify.

The present invention provides an apparatus which eliminates such difficulties in stopping and starting a flashspinning operation. This apparatus comprises a spinneret assembly having a spinning orifice for forming a plexiice filamentary strand and a bafile for spreading the strand into a wide web. The bafile comprises structure defining a smooth arcuate surface positioned to intercept a strand immediately as it exits from the spinning orifice. The baflie further includes structure defining an interior passage-way disposed in heat exchange relationship with the arcuate surface and adapted to receive a coolant.

FIGURE 1 is a schematic illustration, partially in crosssection, of a spinneret assembly and stationary baffle arrangement of the invention showing a water cooling system.

FIGURE 2 is a schematic illustration, partially in crosssection, showing a cooled oscillatable battle in position opposite a flash-spinning orifice.

As shown in FIGURE 1, a solution 1 of a fiber-forming organic polymer (for example linear polyethylene in trichlorofluoromethane) is continuously provided to spinneret 2, at a temperature above the boiling point of the solvent and at autogenous pressure or greater. The spinneret may have a pressure let-down orifice 3 to promote bubble nucleation. The solution then passes through spinning orifice 4 whereupon the solvent evaporates instantly forming a continuous fibrillated strand 5. Immediately following discharge from the orifice the strand is intercepted by entry surface 6 of the baflle 7. The action of expanding gaseous solvent combined with the change in direction provided by the curvature of smooth baflle inner surface 8 causes the fi'brillated strand to spread into a plexifilament Web which (is about 0.1 to 0.5 inch wide at its widest point beyond the baffle for each lb./hr. of polymer throughput. The spreading action takes place as the fibrillated strand passes around the arcuate inner surface 8 of the baflle, which is contiguous with the entry surface 6, as well as with the forward or terminal area 9.

A flat carbon filled polytetrafluoroethylene tumbler 10 prevents the accumulation of polymeric material between the baflle and the spinneret and provides a lubricated juncture between the two pieces. The tumbler is held in place by a cavity 15 in the bafile and pressurized by spring 16 which forces the flat end of the tumbler against the flat spinneret surface 17. The baflle surface is cooled, how ever, by cold water which is introduced through fluid conduit 11 to interior cooling passageway 12 from a source, not shown. Water leaves the baffle through fluid conduit 13. The passageway 12 must, of course, be in heat exchange relationship with the arcuate baffle surface. It may be located directly behind that surface or in associated parts of the bafile as will be shown in FIGURE 2. It will be apparent that cold air or other heat exchange fluids could be pumped through the passageway in place of cold water. The temperature of the baflie 7 may be determined by a thermocouple in well 14.

In the cooled oscillatable baffle of FIGURE 2, parts which are common with those of FIGURE 1 are numbered the same. Cooling is provided here for the arcuate baffle surface via cooling passageway 20 in bearing 21. Heat is removed from the bafiie through oscillating shaft 22 and bearing surface 23. Water flows through the bearing from fluid conduit 24 and is removed by fluid conduit 25. Temperature is kept below C. and is measured via thermocouple 26. By a motor, not shown, the shaft is caused to rotate back and forth through an arc of 5 to 45 depending on solvent temperature and pressure and distance from a collecting belt (not shown). In this embodiment of the invention the coolant serves to prevent fouling of the bafile in several ways. By 'preventing a heat build-up in the bearing 23 it keeps that heat from being transmitted to the arcuate baflie surface. Also any heat that might be transmitted along shaft 22 is withdrawn. Of course, the eifect of any heated gases in the vicinity of the baflle are also overcome.

The amount of coolant is further minimized by the cooling obtained from expanding gases during operation. During shut-down of the solution supply line, however, it is essential to have a cooling fluid passing through the interior cooling passageway of the baffie. The baflie should be kept at a temperature below 100 C. during shut-down and start-up as radiation or conduction from the nearby apparatus causes heat-up. The provision of a cooling stream in the baffie prevents polymer from sticking to the arcuate baffle surface.

The entry surface of the baffie is oriented so as to form a very low angle, i.e. about with the axis of the orifice. The entry surface 6 is contiguous with a smooth curved inner surface 8 which has a radius between about inch and inch, which is contiguous in turn with an exit area or surface 9 arranged preferably at an angle of 60 to 70 relative to the axis of the orifice. The baflle, of course, may be oscillated, and it is preferable to do so when wide sheets are desired with multidirectional laydown of webs. The axis of baffle oscillation is preferably aligned with the orifice axis.

The utilization of a cooled b aille in accordance with the invention has been found in some instances to result in a distinct Widening of the spinning web. In general the bafile temperature should be kept below 100 C. to provide maximum web spreading. Although the reasons for these changes in web width with baffle temperature are not clearly understood, it appears that the amount of tribo electric charge generated is affected by the temperature of the baffie. Increases in temperature of the surface may tend to reduce the amount of tribo charge imparted to the threadline. When the film-fibrils making up the Web are kept cool, a greater tribo charge is retained, and the film-fibrils repel each other, yielding a wider web.

What is claimed is:

1. Flash spinning apparatus for forming a plexifilamentary strand comprising a spinneret assembly and a bafile mounted for oscillatory movement, said spinneret assembly comprising structure defining a spinning Orifice, said bafile comprising structure defining a smooth arcuate surface positioned to intercept a strand imediately as it exits from said spinning orifice, said baflie further including structure defining an interior passageway disposed in heat exchange relationship with said arcuate surface and adapted to receive a heat exchange fluid.

2. Flash spinning apparatus of claim 1 wherein said arcuate surface has a terminal area disposed at an angle of to with respect to the axis of said orifice.

References Cited by the Examiner UNITED STATES PATENTS 2,515,738 7/1950 Slayter et al. 2,723,424 11/ 1955 Veit 18--l2 2,736,676 2/1956 Frickert 161-72 WILLIAM J. STEPHENSON, Primary Examiner. 

1. FLASH SPINNING APPARATUS FOR FORMING A PLEXIFILAMENTARY STRAND COMPRISING A SPINNERET ASSEMBLY AND A BAFFLE MOUNTED FOR OSICILLATORY MOVEMENT, SAID SPINNERET ASSEMBLY COMPRISING STRUCTURE DEFINING A SPINNING ORIFICE, SAID BAFFLE COMPRISING STRUCTURE DEFINING A SMOOTH ARCUATE SURFACE POSITIONED TO INTERCEPT A STRAND IMMEDIATELY AS IT EXITS FROM SAID SPINNING ORIFICE, SAID BAFFLE FURTHER INCLUDING STRUCTURE DEFINING AN INTERIOR PASSAGEWAY DISPOSED IN HEAT EXCHANGE RELATIONSHIP WITH SAID ARCUATE SURFACE AND ADAPTED TO RECEIVE A HEAR EXCHANGE FLUID. 